“Misting” is the term popularly applied to the formation of small airborne droplets of ink that are ejected from the rotating rollers of printing machines. Misting not only wastes ink, it represents a health hazard to workers in the printing industry and requires extraordinary measures in order to keep the printing presses and the rooms in which they are housed clean.
Many workers have investigated the problem and many solutions have been proposed. Some of these are described, for example, in Newspaper Techniques, April 2002, 52-54; GATFWorld, March/April 1996, 8(2), 11, 12; “Factors affecting the misting of UV curable inks”, Hutchinson I D; Richards A M [Paper presented at RadTech Europe, Maastricht, 25-27 September 1995, 231-241]; American Ink Maker, March 1979, 57(3), 47, 48, 52, 54, 108-112. As can be seen, for example, in the last of these documents, a large number of factors are implicated in misting and many different expedients have been adopted in an effort to reduce or eliminate it, including altering process variables, environmental conditions and various elements of the ink composition.
Much of the prior art has emphasized specific compositional changes effect the degree of misting. Some discuss misting as a runnability issue. See, for instance, US Patent Publications 2005/209397, and 2006/0213393; U.S. Pat. Nos. 4,310,356, 5,000,787, and 5,763,565 and WO 2006/042033. Likewise, many articles focus their attention on finding ways to reduce the misting. See, e.g., Traber, K., Has, M. and Dolezalek, F., “Heat balance in web offset printing units,” Taga Proceedings, 279-296 (1993); Voet, A., “Ink misting and its prevention,” American Ink Maker, 34, 32 (1956); Leach, R. H., Pierce, R. J., Hickman, E. P., Mackenzie, M. J. and Smith, H. G., The Printing Ink Manual, 5th Ed. (Blueprint, London, 1993); Christiansen, S., “Resins are gaining weight,” American Ink Maker, 73, 13, 14-60 (1995); James, D. F., Yogachandran, N. and Roper, J. A., III, “Fluid elasticity in extension, measured by a new technique, correlates with misting,” TAPPI Adv. Coating Fundamentals Symp., 8th, Chicago, Ill., 166-171 (May 8-10, 2003); Ascanio, G., Carreau, P. J. and Tanguy, P. A., Non-Newtonian effects on forward deformable roll coating at high speed, In (Eds.) (University Report 833, Paprican, 2003); and McKay, R. C., “Effectiveness of pigments in suppression of misting of lithographic printing inks,” FATIPEC Congress, Paris, France, 22, 137-150 (1994).
Selecting or designing an ink that does not exhibit such a propensity to misting has been a hit or miss proposition since there are no guidelines to help to identify in advance those inks exhibiting reduced misting. This has become more of a problem in recent years due to advances in printing technology.
Recent technological advancements have included the manufacturing and employment of printing presses that operate at high speeds, that is, routine speeds of higher than about 10 m/s (36 km/h or 22.4 miles/h) and up to 15 m/s. This is partly a response to the increased demand for on-time information delivery to more and more customers. These new high speed presses present challenges to the ink manufacturers as their products are being subjected to new stresses during flow. Previous ink formulations that worked well can be unsuitable at the higher speeds. In addition, as the printing machines have begun to operate at increasingly high speeds, the problem of misting has become more pronounced.
A similar misting problem is found in paper coating industry since metering-size presses works on the very same principle of transferring coating color (instead of ink) onto a substrate (paper, cardboard, etc.).